linux-kernel - [PATCHSET 0/6] perf tools: A couple of fixes for perf record --off-cpu (v1)

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Message-Id: <20220624231313.367909-1-namhyung@kernel.org>
Date:   Fri, 24 Jun 2022 16:13:07 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, Song Liu <songliubraving@...com>,
        Hao Luo <haoluo@...gle.com>,
        Milian Wolff <milian.wolff@...b.com>, bpf@...r.kernel.org,
        Blake Jones <blakejones@...gle.com>
Subject: [PATCHSET 0/6] perf tools: A couple of fixes for perf record --off-cpu (v1)

Hello,

The first patch fixes a build error on old kernels which has
task_struct->state field that is renamed to __state.  Actually I made
a mistake when I wrote the code and assumed new kernel version.

The second patch is to prevent invalid sample synthesize by
disallowing unsupported sample types.

The rest of the series implements inheritance of offcpu events for the
child processes.  Unlike perf events, BPF cannot know which task it
should track except for ones set in a BPF map at the beginning.  Add
another BPF program to the fork path and add the process id to the
map if the parent is tracked.

With this change, it can get the correct off-cpu events for child
processes.  I've tested it with perf bench sched messaging which
creates a lot of processes.

  $ sudo perf record -e dummy --off-cpu -- perf bench sched messaging
  # Running 'sched/messaging' benchmark:
  # 20 sender and receiver processes per group
  # 10 groups == 400 processes run

       Total time: 0.196 [sec]
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.178 MB perf.data (851 samples) ]

  $ sudo perf report --stat | grep -A1 offcpu
  offcpu-time stats:
            SAMPLE events:        851

The benchmark passes messages by read/write and it creates off-cpu
events.  With 400 processes, we can see more than 800 events.

The child process tracking is also enabled when -p option is given.
But -t option does NOT as it only cares about the specific threads.
It may be different what perf_event does now, but I think it makes
more sense.

You can get it from 'perf/offcpu-child-v1' branch in my tree

  https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git

Thanks,
Namhyung

Namhyung Kim (6):
  perf offcpu: Fix a build failure on old kernels
  perf offcpu: Accept allowed sample types only
  perf offcpu: Check process id for the given workload
  perf offcpu: Parse process id separately
  perf offcpu: Track child processes
  perf offcpu: Update offcpu test for child process

 tools/perf/tests/shell/record_offcpu.sh | 57 ++++++++++++++++++++---
 tools/perf/util/bpf_off_cpu.c           | 60 +++++++++++++++++++++++--
 tools/perf/util/bpf_skel/off_cpu.bpf.c  | 58 +++++++++++++++++++++---
 tools/perf/util/evsel.c                 |  9 ++++
 tools/perf/util/off_cpu.h               |  9 ++++
 5 files changed, 176 insertions(+), 17 deletions(-)

base-commit: 9886142c7a2226439c1e3f7d9b69f9c7094c3ef6
-- 
2.37.0.rc0.161.g10f37bed90-goog